1. Field of the Invention
The present invention relates to a motor and a method for manufacturing the same, and in particular, relates to a motor having figure 8-shaped linked coils and a method for manufacturing the same.
2. Description of the Related Art
As a combination of poles and slots enabling the cogging torque and the torque ripple to be reduced, there is conventionally known a motor having the “fractional slot” configuration where the number of slots divided by the number of poles is an irreducible fraction.
In a fractional slot type motor, it is possible to select the number of poles and the number of slots so as to increase the least common multiple of the number of poles and the number of slots and is possible to set a small value of high-order distributed winding coefficient, thereby enabling the cogging torque and the torque ripple to be reduced (e.g. see Japanese Patent Application No. 2014-125680).
In a motor in which the number of slots 6N is more than 1.5 times but less than 3 times the number of pole pairs P (1.5P<6N<3P), the motor is a concentrated winding motor of which the slot pitch is 1. In this case, since it is possible to wind coils around adjacent slots, the coils can be directly wound (i.e., direct winding) around the teeth of the stator using a nozzle of the winding machine. This is very advantageous for production. However, since the number of slots is relatively small, the magnetic flux lines generated in the rotor and the stator are susceptible to the teeth shape of the stator or the external shape of the stator core and thus deteriorate the levels of the cogging torque and the torque ripple. This results in the limited advantageous effects in even the fractional slot configuration.
On the other hand, in a fractional slot type motor in which the number of slots 6N is more than 3 times the number of pole pairs P (6N>3P), the cogging torque and the torque ripple tend to become smaller than in a concentrated winding motor of fractional slot configuration, which is appealing in terms of performance. However, the coil pitch of the windings to be inserted into the slots is larger than 1 slot and winding is only possible by distributed winding. In particular, in a motor where the number of slots divided by the number of pole pairs is an irreducible fraction, the layout of the windings is complicated and therefore takes a large number of coils of windings to be inserted into the slots. This is not suited for automation of winding at the time of production.
In addition, the large number of coils increases crossover lines connecting the coils, causing the complicated arrangement of the windings.
As an example, in an inserter type automatic winding machine, a nozzle or a flyer of the winding machine rotates around winding frames to produce coils one by one, the coils thus produced are inserted into the inserter, and the inserter is gradually pushed into the stator, thereby winding the coils around the stator. In this process, if a large number of coils are produced, the number of times of insertion into the inserter increases, resulting in the great number of production steps. Further, since a large number of coils are inserted into the inserter, the large number of crossover lines between the coils makes a complicated arrangement of the windings, causing the manufacturing failure.
Thus, a fractional slot type motor having a complicated winding layout has the following problems when winding is performed by automatically windable concentric winding.
(1) The number of coils is large and, as a result, increases the number of production steps.
(2) The number of crossover lines connecting the coils is large and causes a complicated arrangement.